KR100202075B1 - Process for producing foamable particles of styrenic polymers - Google Patents

Abstract

A method of making styrene polymer foamable particles, which consists of losing some blowing agent in an oven at a temperature lower than the glass transition temperature (Tg) of the particles.

Description

Process for producing styrenic polymer foam particles with improved processability and mechanical properties

The present invention relates to a method for producing styrenic polymer foam particles having improved processability and mechanical properties.

More specifically, the present invention provides the production of styrenic polymer foamable particles suitable for producing finished products and blocks having excellent surface appearance, low shrinkage, high sintering degree and relatively short residence time in the mold by molding. It is about a method.

The production of styrenic polymers, in particular polystyrene foam particles, is known in the art. The process consists of incorporating a blowing agent into the polymer that boils at a temperature below the softening point of the polymer during or after the polymerization step.

When the particles containing the blowing agent are heated, the blowing agent evaporates to form a number of closed hallows, or cells, in the polymer.

In order to produce a low density finished product or block, these particles are placed in an empty space of a mold defined by the desired finished product shape, and then heated to a temperature higher than the softening point of the polymeric material and the boiling point of the blowing agent. During this heating step the particles are foamed, and because of the limited space, a body is formed with the shape and size of the mold used.

The particles can be injected directly into the mold or pre-formed before injection into the mold and can be aged for about 15-30 hours.

After molding, the molded product is cooled in the mold for a sufficiently long time so that the molding after de-moulding does not deform.

Since the foamed plastic material is a very good thermal insulator, it requires a relatively long residence time in the mold to cool the molded body.

Therefore, the cooling time represents a large part of the molding cycle and significantly reduces the molding throughput for a given time.

In order to reduce the residence time in the mold and at the same time obtain good sintering results, in the past, small amounts of halogenated organic compounds, such as bromo-, chloro- or chloro-bromo derivatives, have been added to the styrene-based polymer during polymerization. Has been proposed.

Some examples of these organic compounds added to styrene during the polymerization step are described in US Pat. No. 4,169,193; 4,172,928; And 4,200,696.

These organic products can reduce the residence time in the mold to a significant extent, but there are some disadvantages that limit their use. The first disadvantage is the development of an unpleasant odor during the pre-expanding stage. In addition, the shrinkage ratio after molding is high, and as a result, a molded body of a previously planned size cannot be obtained.

In addition, the use of halogenated organic products can cause toxic problems when the material is used for food packaging. As is known, various national legal regulations suggest that halogenated products should be removed from the expandable polystyrene formulation.

European Patent Publication No. 0 046 494 proposes coating styrene polymer particles with hydroxycarboxylic acid esters or carboxylic acid esters of alkoxy alcohols. This coating gives very short time and very good sintering ability to the material, but in order to obtain satisfactory results with the problem that the particles harden in the container and contaminate the treated water during the molding operation, a large amount of additives are added to the particles. Indicates a disadvantage.

Applicants have found that styrene-based polymer foam particles suitable for obtaining molded articles that do not exhibit the above-mentioned drawbacks include styrene-based polymer foam particles containing 2 to 20% by weight of blowing agent before pre-foaming at a temperature below the glass transition temperature of the particles. It has been found that this can be obtained by losing some blowing agent at.

Therefore, an object of the present invention is to provide a styrene-based polymer foamable particle suitable for producing a molded article and a block by molding, in particular, having excellent surface appearance, low shrinkage rate, and a relatively short residence time in the mold. ,

Preparing styrenic polymer expandable particles containing 2-20% by weight of blowing agent incorporated;

Coating the particles with up to 1% by weight of an antistatic agent;

A process consisting in removing some of the blowing agent incorporated at a temperature below the glass transition temperature of the particles.

The amount of blowing agent removed from the foamable particles is not effective for the purposes of the present invention, but especially in terms of sintering degree, the loss ratio of the blowing agent is not more than 60% by weight, preferably 5-50% by weight relative to the initial content of the blowing agent. The best results are obtained when it is contained.

Removal of the blowing agent is preferably carried out by heating at a temperature lower than the glass transition temperature (Tg) of the particles, preferably by heating in an oven.

The residence time of the particles in the oven varies with the temperature and the amount of blowing agent removed. Generally, the temperature is 25 to 60 , Preferably 35 50 The residence time is 10 minutes to 24 hours.

Particles containing a blowing agent can be prepared by polymerizing styrene alone or one or more ethylenically unsaturated comonomers copolymerizable with styrene in the presence of a blowing agent, preferably in an aqueous suspension.

It is known from the prior art that the polymerization can be carried out in the presence of one or more peroxy initiators or by thermal methods according to conventional methods.

According to another method, the foaming agent can be incorporated into the previously prepared styrene-based polymer by exposing the polymer particles to the vapor phase of the blowing agent, or by adding the blowing agent to already prepared particles suspended in water or during the extrusion step. have. Various methods of producing expandable particles are already known in the art and described in the technical literature. See, eg, British Patent 695,826; 715,100; 886,811; 908,089; 1,048,243; And US Pat. No. 2,983,692, the contents of which are incorporated by reference.

As used in the entire specification and the appended claims, the expression styrene polymer or styrene-based polymer refers to styrene homopolymers and other vinyl- and / or vinylidene-based monomers containing at least 50% by weight of chemically bound styrene. It means styrene copolymer of.

Examples of such comonomers are Methyl styrene; Halogenated styrenes such as 2,4-dichlorostyrene; Acrylonitrile; Methacrylonitrile; Such as esters of acrylic acid and / or methacrylic acid , Esters of unsaturated carboxylic acids with C ₁ to C ₈ alcohols; N-vinyl compounds, such as vinylcarbazole, etc. are mentioned.

The expression styrene polymer or styrene polymer includes, in addition to styrene, a copolymer containing a small amount of monomer having two double bonds in the form of vinyl, such as the vinyl and / or vinylidene-based comonomers described above, and divinylbenzene. Also included.

The expandable polystyrene particles, as blowing agents, may be in gaseous or liquid form at room temperature and do not dissolve the polymer, but because they foam, they contain conventional easy volatile organic compounds having a boiling point below the softening point of the polymer.

Examples of particularly suitable blowing agents include aliphatic hydrocarbons having 2 to 6 carbon atoms, such as propane, butane, n-pentane, isopentane, hexane, cyclohexane and the like, which can be used alone or as a mixture; Petroleum ether; C such as various chloro- and fluoro- derivatives of methane, ethane and ethylene, such as dichloro-difluoromethane, 1,2,2-trifluoro-ethane, 1,1,2-trifluoro-ethane and the like Halogenated derivatives of ₁ to C ₃ aliphatic hydrocarbons.

Blowing agents are generally used in amounts of from 2 to 20% by weight, preferably from 4 to 10% by weight, based on the weight of the polymer.

Antistatic agents used in the process of the present invention are generally used to improve the free-flowing surface, finish and processability of styrenic polymer particles.

Antistatic agents are known and described in the technical literature; For example, [K. Johnson, Antistatic Compositions for Textiles and Plastics, Noyes Data Corporation, Park Ridge N. J. 1976.

Examples of antistatic agents that can be used in the process of the invention include fatty acid esters such as butyl stearate; Mono-hydroxy or poly-hydroxy alcohols such as glycerol; Amines such as ethoxylated tertiary alkylamines and fatty acid dialkanolamines; Amides such as N, N-bis- (2-hydroxyethylstearicamide); Polyoxyethylene or polyoxyalkylene derivatives such as polyethylene glycol hexadecyl ether; Ethylene oxide / propylene oxide copolymers; Amine soaps such as stearic acid salt of octadecylamine; Amine salts of alkyl-sulfates, such as octadecyl sulfate salts of guanine; Quaternary ammonium compounds such as octadecyl-trimethyl-ammonium chloride; Alkyl-phosphates such as bisdodecyl hydrogen phosphate; And amine salts of alkyl-phosphonic acids such as octadecyl-phosphonic acid salts of triethanolamine.

Such antistatic agents may be used alone or as a mixture in any ratio.

Preferred antistatic agents used in the process according to the invention are block ethylene oxide / propylene oxide blocks sold under the trade name GLENDION ^{(R) with} a content of 10-50% by weight of ethylene oxide and a molecular weight of 1000-5000. Copolymer; Or an ethoxylated tertiary alkyl amine sold under the trade name ATMER ^(R) by ICI.

Generally, the amount of the antistatic agent is 1% by weight or less, for example, 0.001 to 0.5% by weight, and preferably 0.010 to 0.1% by weight relative to the polymer.

The polymer particles may be coated with the antistatic agent by any mixing method as known in the art; For example, the expandable particles may be treated with an appropriate amount of antistatic agent in a rotating drum or tumbler.

By coating the particles with antistatic agents, different fractions are obtained, each facilitating subsequent sieving operations, each having a controlled size range and conferring various uses.

Before entering the forming step, the particles are subjected to a prefoaming step by steam or hot air at a temperature higher than the glass transition temperature of the particles according to methods known in the prior art, and then aged at room temperature for 10-30 hours.

The expandable particles obtained by the process according to the invention exhibit the following properties;

(a) a short residence time in the mold, generally equal to or less than 50% of the time required to cool the blocks or shaped articles produced from prefoamed particles not treated by the process according to the invention;

(b) 1% or less in the deformation and thickness direction of the block;

(c) molding is carried out by adding a high sintering degree, a significant amount of recycled waste foam product;

(d) short ripening time after pre-expanding;

(e) High absorption of pigments or other adhesives on the surface.

In addition to blowing agents, styrene polymers may contain additives such as flame retardants, oil and inorganic fillers, dyes, pigments, antistatic agents, anti-agglomerating agents, plasticizers and other similar compounds to prevent agglomeration formed during the pre-foaming step.

Conversion of the particles into shaped articles, preferably by addition of a blowing agent during the polymerization, preferably by the addition of the blowing agent in an aqueous suspension and molding in a closed mold, is a technique known to those skilled in the art. And TN Ferrigno, Rigid Plastic Foams, Reinhold Publishing Corp., New York, USA (1963)] is widely described in the technical literature.

The following examples are set forth for the purpose of better illustrating the important features of the present invention and are in no way intended to limit the present invention.

Example 1

85-120 Styrene was polymerized in the presence of dibenzoylperoxide and tert-butyl peroxide as catalysts in an aqueous suspension of 2.7 Phosphorus 20 To obtain polystyrene particles.

Particles exiting the polymerization reactor were washed with water, centrifuged and Dry for 1 hour at.

The expandable particles are mixed with a 300 ppm antistatic agent, which is composed of a block copolymer of ethylene oxide and propylene oxide in a 10:90 weight ratio, and commercially available under the trade name GLENDION FG having a molecular weight of 2000 to 3000.

Mixing is performed for about 10 minutes at room temperature in a tumbler. The particles are then sieved (A) with a diameter of 0.4-0.9 Fraction consisting of phosphorus particles, and (B) a diameter of 0.9 to 2.7 Separate into two fractions of the fraction consisting of phosphorus particles.

The content of blowing agent measured for each fraction was 6.8% by weight in fraction (A) and 6.9% by weight in fraction (B).

Each fraction is divided into two identical portions, namely A.1 and A.2; Subdivide into B.1 and B.2.

Fraction A.2 is placed in an oven, about 35 Heated to 10 minutes and the content of blowing agent is measured. When the content of blowing agent reaches 5% by weight, the sample is taken out of the oven and rapidly cooled to prevent loss of blowing agent.

Each fraction A.1 and A.2 is usually composed of about 25 g / g of 0.2% by weight of glyceryl monostearate and 0.05% by weight of zinc stearate relative to the polymer weight Shall be. Each fraction is aged in air at room temperature for 24 hours, then shaped to form 40 60 And thickness is 2 Switch to phosphorus packaging container. Molding is carried out using 0.9 Ate of steam. The cooling time of the vessel, which is defined as the residence time in the mold required to maintain the size of the mold after each molding has been extracted from the same mold, is measured.

The vessel obtained from fraction A.2 exhibits a cooling time (2 minutes 45 seconds) which is about 50% shorter than the cooling time (5 minutes) of the vessel obtained from fraction A.1.

For each vessel, the degree of sintering, which is defined as the percentage of foamed particles that break after the vessel bottom is damaged, is determined.

Sintered percentage is about 10 The damage area of the surface area of ² is defined, and the number of damaged particles is calculated by counting the total number of particles contained in the area against the total number of particles.

By this measurement, the sintering degree of the container from A.1 is 15%, while the sintering degree of the container from A.2 is 80%.

Fraction B.2 is treated as described for fraction A.2. When the blowing agent content is 5.1%, the sample is removed from the oven and rapidly cooled to stop the loss of blowing agent.

B.1 and B.2 Each fraction is mixed with the same coating agent as used in fractions A.1 and A.2, as in fractions A.1 and A.2 above, and the density is about 20 g / Prefoam and mature at room temperature for 24 hours.

Each fraction was then molded to 100 100 50 Obtain a block of. Molding is carried out using 0.65 Ate steam.

The residence time in the mold of the block obtained from fraction B.2 (9 minutes) is 55% shorter than the residence time in the mold of the block obtained from fraction B.1 (20 minutes).

The deformation measured for the thickness of the blocks obtained from fraction B.2 is 75% lower than the thickness of the blocks obtained from fraction B.1 (5 Teen 20 ).

5 cut from fraction B.2 block The sintering degree of the sheet of thickness is of much higher (50% vs. 5%) than the corresponding sheet cut into blocks from fraction B.1.

From blocks, thickness 1.5 Cut the sheet of paper. When these were examined against a dark background, the block-derived sheet obtained from fraction B.2 had no cracks between the sintered particles, whereas the block-derived sheet obtained from fraction B.1 was found to be cracked. .

Example 2

Except that the aging time is 5 hours, the treatment is performed on both fractions A.1 and A.2 of Example 1 under the same operating conditions as in Example 1.

The treatment time in the mold of the vessel obtained from A.1 is at least 10 minutes and is much more deformed after removal from the mold. The residence time in the mold represented by the vessel obtained from fraction A.2 is only about 20% longer than that of Example 1, which was aged for 24 hours; In addition, the breakout vessel is not deformed.

Example 3

After aging for 24 hours, fractions B.1 and B.2 obtained in Example 1 are mixed with 25% by weight of foamed polystyrene recovered from the waste material obtained by grinding the crushed molded article.

Each fraction is molded under the same conditions as in Example 1.

The sintering degree of the blocks from fraction B.2 is much higher than the sintering degree of the blocks from fraction B.1 (40% vs 0%).

In addition, when visually irradiated against a dark background, 1.5 delivered using hot wire from the block obtained from fraction B.2. The sheet of thickness is generally free of cracks between the sintered particles.

Similar sheets obtained by cutting the blocks obtained from fraction B.1 are not flat and have large cracks and condensate clearly attached.

Example 4

In the same manner as shown in Example 1, two samples C.I and C.2 are prepared which are identical to the characteristics of Samples A.1 and A.2 of Example 1, respectively.

Each sample is mixed with 0.1 wt% carbon black and then mixed with a conventional molding coating agent consisting of 0.2 wt% glyceryl monostearate and 0.05 wt% zinc stearate relative to the polymer.

Mixing is performed in a tumbler at room temperature.

Each sample is prefoamed, aged and shaped under the same operating conditions as in Example 1.

Sample C.2 has a uniformly colored surface without the release of carbon black; In contrast, the C.1 sample has an uneven distribution of carbon black and loses pigment over time.

In addition, the sintering degree of the molded article obtained from sample C.2 is much higher (25% vs. 0%) than the molded article obtained from C.1.

Claims (15)

Improved processability and mechanical properties, characterized by the loss of some blowing agent at temperatures below the glass transition temperature of the particles, prior to prefoaming the styrenic polymer foaming particles containing 2 to 20% by weight of blowing agent. Method for producing styrenic polymer foam particles. The method according to claim 1, wherein styrene-based polymer foam particles containing 2 to 20% by weight of blowing agent incorporated are prepared:-coating the particles with up to 1% by weight of an antistatic agent; A process for removing part of the blowing agent incorporated at a temperature below the glass transition temperature of the particles. The production method according to claim 1 or 2, wherein the loss amount of the blowing agent is 60% by weight or less based on the initial content of the blowing agent. The method according to claim 1 or 2, wherein the removal of the blowing agent is 25 to 60. The production process is carried out for a residence time of 10 minutes to 24 hours at a temperature of. The compound of claim 1 or 2, wherein the blowing agent is a compound or a mixture of each of C ₂ to C ₆ aliphatic hydrocarbons such as propane, butane, n-pentane, isopentane, hexane, cyclohexane and the like; Petroleum ethers; And halogenated derivatives of C ₁ -C ₃ aliphatic hydrocarbons such as methane, ethane and ethylene chloro- and fluoro- derivatives. The manufacturing method of Claim 1 or 2 in which a foaming agent contains 4 to 10 weight% with respect to the weight of a polymer. The antistatic agent according to claim 1 or 2, wherein the antistatic agent is selected from fatty acid esters such as butyl stearate; Mono-hydroxy or poly-hydroxy alcohols such as glycerol; Amines such as ethoxylated tertiary alkylamines and fatty acid dialkanolamines; Amides such as N, N-bis- (2-hydroxyethylstearicamide); Polyoxyethylene or polyoxyalkylene derivatives such as polyethylene glycol hexadecyl ether; Ethylene oxide / propylene oxide copolymers; Amine soaps such as stearic acid salt of octadecylamine; Amine salts of alkyl-sulfates, such as octadecylsulfate salts of guanidine; Quaternary ammonium compounds such as octadecyl-trimethyl-ammonium chloride; Alkyl-phosphates such as bisdodecyl hydrogen phosphate; And amine salts of alkyl-phosphonic acids, such as octadecyl-phosphonic acid salts of triethanolamine, and are used as respective compounds or as mixtures in any proportion. 8. The process according to claim 7, wherein the antistatic agent is an ethylene oxide-propylene oxide block copolymer having a content of ethylene oxide of 10 to 50% by weight and a molecular weight of 1000 to 5000. 8. The process of claim 7, wherein the antistatic agent is an ethoxylated tertiary alkylamine. The production method according to claim 1 or 2, wherein the amount of the antistatic agent is 0.001 to 0.5% by weight based on the weight of the polymer. The process according to claim 1 or 2, wherein the styrenic polymer foam particles are sieved before the foam particles are partially removed. Styrenic polymer foamable particles obtained by the process according to claim 1. The method according to claim 3, wherein the loss amount of the blowing agent is 5 to 50% by weight relative to the initial content of the blowing agent. The method of claim 4, wherein the removal of the blowing agent is 35-50 The production method is carried out at a temperature of. The production method according to claim 10, wherein the amount of the antistatic agent is 0.01 to 0.1% by weight based on the weight of the polymer.